A fuel cell system is a power generation system in which fuel is oxidized through an electrochemical process, thereby directly converting energy discharged as a result of the resultant oxidation reaction into electrical energy, and the fuel cell system has a stack structure which is constituted from a plurality of membrane/electrode assemblies each having a configuration in which an electrolyte membrane for selectively transporting hydrogen ions is sandwiched, on both of its sides, by a pair of electrodes formed of a porous material. In particular, a solid polymer electrolyte fuel cell, in which a solid polymer membrane is used as an electrolyte, can easily be reduced in size at a low cost and has a high output density, and therefore is expected to be used as a vehicle-mounted power source.
In this type of fuel cell, the optimum temperature range for power generation is generally considered to be from 70 to 80° C. However, in, e.g., a cold environment, a long time might be required from when the fuel cell is started until the temperature of the fuel cell reaches the optimum temperature range. Therefore, various warm-up systems have been under consideration. For example, JP2004-030979 A discloses a method in which a low-efficiency operation with a low power generation efficiency compared with a normal operation is carried out to control the self-heating power of a fuel cell in order to warm up the fuel cell. This method attains a self warm-up of the fuel cell, and therefore, a warm-up device does not need to be provided, which is excellent in terms of convenience.
Patent Document 1: Japanese laid-open patent publication No. 2004-030979